7 Volcanoes We Should Be Watching

Two years ago, Iceland's Eyjafjallajökull brought most European air travel to a halt. This year, volcanoes such as Mexico's Popocatépetl and Indonesia's Lokon-Empung are rumbling. Volcanoes are impossible to predict with certainty, but these are seven active ones that we know we must watch.

Popocatépetl, Mexico

Popocatépetl, Mexico

Forty-three miles southeast of Mexico City, 17,802-foot Popocatépetl (the name means smoking mountain) lay dormant the first half of the 20th century but has been increasing in activity since the early 1990s, when it exploded in a plume of gas and ash that carried more than 15 miles.

Now "Popo" is rumbling again. In April, the volcano put on a show of glowing rock and spewing vapor. At some points the volcano even emitted a low-pitch roar, blasting ash upward and hurling superheated rock fragments into the air—a result of built-up pressure from magma beneath its slopes.

Popocatépetl is a stratovolcano, a type that is conical in shape and produces thick, slow-moving lava, which scientists say is unlikely to do much physical damage to the area. Still, if Popocatépetl continues to gush ash clouds and steam plumes, it could wreck havoc on air travel to and from Mexico City and dislocate tens of thousands of nearby residents—particularly in the area's farming villages.

Indonesia's Lokon-Empung

Indonesia's Lokon-Empung

Rising off the island of Sulawesi, twin-peaked Lokon-Empung is one of Indonesia's most active volcanoes. The 5184-foot Lokon peak is the older and flatter of the two; neighboring Empung is young and is topped with a crater that stretches more than 1300 feet across and nearly 500 feet deep.

These two peaks are relatively inactive—it's the double crater between them, Tompaluan, that keeps residents on their toes. Since the mid-19th century, Tompaluan has exploded in phreatic eruptions that are a mix of steam, water, ash, rock, and " volcanic bombs,"—hunks of molten rock that cool before landing. Tompaluan also produces the occasional lava flow.

This past month, the volcano began emitting a series of loud thumping noises and white plumes of vapor that rise more than 300 feet above Tompaluan crater, raising the volcano's alert level to three (four means an eruption is eminent). Last week it let out an 8000-foot plume, and the government has begun to set up evacuation centers.